Traffic between the nucleus and cytoplasm must pass through the elaborate and highly regulated nuclear pore complex, which thus serves as a gateway to the genome. Normal traffic includes all signals from the outside world, reworded into a language that evokes nuclear change. Traffic outward includes messages designed to translate this nuclear change into action. A study of disease reveals that viruses, including HIV, influenza, polio, and SV40, have evolved mechanisms to hit right at the heart of the nuclear pore and nuclear transport. Inherited human diseases, such as the Nup98- and Nup214-linked human leukemias, result from disruption of these nucleoporin genes. To understand the ways in which disease and viral infection arise from the subversion of normal nuclear trafficking, one must first understand the mechanism of that trafficking. Recently, our lab identified a specific subunit, the Nup 107-160 subcomplex, which is essential to the structure, function, and assembly of the nuclear pore. In the absence of this subcomplex, nuclei are devoid of nuclear pores. The present grant has four major goals: (1) The first is to gain a full molecular and structural knowledge of the critical Nup107-160 complex. This knowledge will be used to decipher complex interactions within the nuclear pore, so that the first three-dimensional map of the elaborate vertebrate nuclear pore may be built. (2) A second goal is to understand the mechanism of nuclear pore assembly, a key event that must occur each cell cycle. The essential nature of the Nup107-160 complex to NPC assembly gives an excellent starting point for this quest. (3) A third goal is to define how an unexpected player, importin beta, not only regulates NPC assembly, but also controls nuclear membrane fusion and assembly. The targets of importin beta in each of these regulatory roles will be sought. (4) A last goal focuses on determining the function of the Nup107- 160 complex on mitotic kinetochores. Successful completion should provide essential insight into the vital gateway to the nucleus.